Removed session.currentSession.staffMemberId from POS UI Extensions (2026-10)

As of API version 2026-10, the static session.currentSession.staffMemberId field has been removed from the POS UI Extensions Session API. It was deprecated in 2026-07 in favour of session.staffMember, a reactive signal that updates when a different staff member pins into POS. Before targeting API version 2026-10, replace reads of session.currentSession.staffMemberId with session.staffMember.value?.id.